A variety of medical conditions exist for which ongoing delivery of therapy and/or extended monitoring of the patient's condition is indicated. For example, patients can exhibit medical conditions which indicate extended periods of delivery of therapeutic agents/medications. Patients may also exhibit medical conditions indicating extended stimulation of nerve tissue. Patients may also exhibit a variety of cardiac arrhythmias indicating the ability to monitor the patient's condition and automatically generate and deliver therapeutic stimulations to treat detected arrhythmias. Patients may also exhibit a variety of medical conditions wherein extended monitoring of the patient's physiologic activity can provide valuable diagnostic data to a clinician. However, in general, such information and/or therapy cannot readily or conveniently be obtained/provided via periodic intermittent clinical observations.
In many such circumstances, a clinician can prescribe and arrange for the provision of an appropriate configuration of medical device to provide the indicated therapy and/or monitoring of the patient. Frequently, such medical devices are configured to be at least partially implantable. Implantable structures offer the advantage of extended in situ placement to facilitate delivery of therapy and/or monitoring of physiologic activities at internal locations where access to such locations would otherwise generally require the presence of the patient in a clinical setting and the attention and services of skilled clinical personnel. By providing at least a portion of medical devices in an implantable configuration, the patient is frequently able to at least partially return to a more normal lifestyle while receiving the benefits of therapy delivery and/or diagnostic monitoring at times when they are not in a clinical setting. Implantable devices and structures also offer the advantage to the patient of convenience as the implantable structures are arranged within the patient's body and are not exposed to interference, for example with clothing, and present reduced inconvenience for personal activities such as routine hygiene and physical activity.
Many types of implantable medical devices include lead/electrode structures and/or catheter structures which extend within the patient's body. The lead/electrode or catheter is frequently fixed with respect to patient tissue to facilitate repeatable delivery of indicated therapy and/or measurements of physiologic activity at a desired region of interest. Accordingly, many configurations of implantable devices including patient lead/electrodes and/or catheter structures include provision for fixation to patient tissue. Fixation can be facilitated by sutures, barbs, hooks, and/or a variety of fixation structures.
In a number of implementations, however, there exist difficulties with existing implantable device systems and methods for implantation of such systems in accurately placing and fixing patient leads in desired locations. For example, implantation procedures are frequently performed in a manner such that a fixation location is not easily directly observable by the clinician performing the implantation procedure. Fluoroscopy is one known imaging technique that can be employed by physicians to obtain real-time images of obscured internal structures of a patient and of implantable device structures, including patient leads, to facilitate placement of implantable structures. A fluoroscope generally includes an X-ray source and an imaging screen between which the patient and regions of interest can be arranged. Fluoroscopes can include X-ray image intensifiers and video cameras to facilitate more convenient reviewing and recording of fluoroscope images and to reduce exposure of the patient to ionizing radiation.
One limitation with fluoroscopy however is that it is at least sometimes difficult to accurately discern soft tissue boundaries. This can make it difficult for a clinician to view whether or not an implanted device is at a desired position with respect to target tissue.
Another difficulty with fluoroscopy in positioning of implantable structures is that the obtained image is a two-dimensional image. Thus, while fluoroscopy may be able to relatively accurately provide location information to the clinician in two dimensions orthogonal to the viewing dimension, three-dimensional location information or location information generally along or parallel to the fluoroscopy viewing dimension is less readily discernible. This lack of three-dimensional or “depth” location data can complicate accurate positioning of the implantable structures at the desired location. In addition, as fluoroscopes employ X-ray sources to irradiate the patient tissue and obtain a fluoroscope image, use of fluoroscopy exposes the patient to highly undesirable ionizing radiation. While fluoroscopy can provide highly useful real-time image data, these benefits must be weighed against possible deleterious side effects from exposure to the ionizing radiation.